Time domain reflectometry repeatedly transmits short duration pulses along a cable or line under test (LUT) and examines reflected waveshapes to determine the condition of the LUT. Classically, reflected signals have been observed as a trace on an oscilloscope, requiring a user to make a spot judgement regarding the severity of a potential problem on the LUT.
Modern time domain reflectometers digitally sample a reflected signal waveform, store the sampled digital values, and subsequently analyze the signal's waveshape. To achieve an optimum reproduction of the reflected waveform, a high frequency sample rate is required; however, as the sample frequency rate increases, more sophisticated (and expensive) systems are required to digitize and store these high frequency signals.
To enable the use of lower frequency sample rates while still achieving accurate reflected waveform reproduction, prior art circuits generate many test pulses and sample each succeeding reflection waveform at an increasingly later time in the reflected pulse. By combining all of the sample waveform values over many succeeding test pulses, an accurate waveshape is achieved that is equivalent to one achieved as a result of an extremely high sample rate. Such systems are taught in U.S. Pat. No. 3,244,975 to Bauer and U.S. Pat. No. 4,797,621 to Anderson et al. While achieving highly accurate waveshapes, such systems require successive sampling of many reflected pulse waveforms to achieve an effective high frequency sampling rate. The prior art circuits thus require a substantial time period to process sequential reflection waveforms so as to obtain the desired waveshape. If, during such time period, the condition changes that causes the reflections on the LUT, the resulting signal waveform may be distorted and difficult to analyze.
Accordingly, it is an object of this invention to provide a time domain reflectometry system wherein test signal return synthesis can be accomplished in a short time period.
It is another object of this invention to provide a time domain reflectometry system that manifests a high frequency sample rate and achieves an effective reflected pulse waveform after a few test pulses.
It is still another object of this invention to provide a time domain reflectometry system which employs low frequency data processing circuitry.